The present invention relates to signal filtering, and more particularly to a method of up-sampling half-band reconstruction filtering that has greater computational efficiency in order to have realtime performance in a video waveform monitor.
Reconstruction filters amount to specialized lowpass filters with sin(x)/x impulse responses, and are used for many applications, from digital to analog conversion to interpolation for waveform displays. The most common method of reconstruction is through the used of two-times up-sampling with half-band finite impulse response (FIR) filtering—typically a time windowed sin(x)/x impulse response with the following for improved efficiency:                1) Zero values (even samples of sin(x)/x) ignored;        2) “Folded” architecture, adding input data values before multiplying by common coefficients (taking advantage of symmetry of the impulse response).An example implementation of this method is for digital to analog conversion reconstruction filtering for standard definition video using the Recommendation ITU-R BT.601-5 filter specifications (Appendix 2 to Part A, FIG. 3: Specifications for a luminance or RGB signal filter used when sampling at 13.5 MHz). A typical implementation, as shown in FIG. 1, uses sixteen multiplications and thirty-two additions.        